What is this structure called?

What is the primitive circular stone structure in front of the Washington DC capitol building called?

• When I was young my family visited Washington DC and there was one structure in particular I've been trying to get data and photography of though I've forgotten the name. It's a small stone structure with benches lining the wall and a wrought iron gate but has no roof and seems to be quite old. There may have been a fountain situated in the middle, not sure though. Possibly a monument of sorts, not entirely sure about that either. I forget which direction from the Capitol building it resided but it seemed to be located in a garden area.

• Answer:

  You're probably thinking of the Summer House on the U.S. Capitol grounds (Senate side); the Capitol grounds were designed by Frederick Law Olmsted: "The Summer House, a brick structure set into the sloping hillside of the West Front lawn among the paths that lead from Pennsylvania Avenue to the Senate side of the Capitol, has offered rest and shelter to travelers for over a century. Constructed to provide comfort for those who explore the area on foot, it is also a pleasant location from which to appreciate the Capitol's classical architecture and the landscaping that surrounds it...The Summer House was begun in 1879 and completed in late 1880 or early 1881 by landscape architect Frederick Law Olmsted."